Animal models, principally the chinchilla, will be used to study the relations between steady and intermittent noise exposure and the resulting changes in behavioral auditory capabilities, in electrophysiological characteristics, and in structural and biochemical features. Changes in structure of the stria vascularis and in the constitution of the fluids of the inner ear associated with both temporary and permanent hearing losses will receive particular attention. Analogous studies will involve the action of ototoxic drugs, not only those injected but also those applied topically in the middle ear, and the synergistic action of drugs and noise. Changes in vestibular function associated with drugs that are not only ototoxic but also vestibulotoxic will also be determined. The perception and misperception of auditory stimuli, both pure tones and speech, will be studied very intensively in a relatively small number of human patients with selected specific sensory losses and a few with more central damage; emphasis will be on temporal resolution, frequency discrimination, and pitch perception. Finally, analysis of temporal bones from persons with hearing losses of known etiology will be used to develop techniques for differential diagnosis of types of sensorineural loss.